The invention relates to an improved motor having a magnet retention assembly and more particularly relates to a method of mounting a magnet in a motor frame during assembly of a motor.
Generally, there are two basic methods of mounting a magnet into a motor frame. The first method uses a clip assembly that mechanically fastens the magnet against the cylindrical motor frame by spring pressure. The second method uses various adhesives to secure the magnet against the motor frame.
Clip assemblies used in such an assembly method are especially designed to snap into place and put strong pressure against the arc end of the magnets to hold the magnets against the frame. The clipping operation is a clean and safe production process. It takes a low energy input and as a result is a low cost process.
Although the clipping process lends itself readily to automation, there are some limitations on the process that restrict universal application. The first of these is that clips are restricted generally to a two pole motor construction. The variations in clip pressure make four pole designs impractical. Secondly, the clips provide a limited holding force when compared to magnets which are bonded to the motor frame. Thirdly, the clip field assembly has limited impact resistance due to the limiting holding force of the clips. Finally, clipping requires tighter magnet dimensional tolerencing. Because of these limitations, clips are generally restricted to motor diameters of three inches or less.
The method of adhering magnets to the motor frame makes use of various types of adhesives. Generally, the method involves a manual scrubbing operation to thoroughly clean the frame and a manual application of the activator and resin used to bond the magnets to the frame. A good adhesive bond depends on the quantity, degree of surface coverage and the age of adhesive and resin. This process of bonding must be closely monitored to obtain a consistent bond. Also, during assembly the bonding material must be applied to the motor frame and/or the magnet and special fixturing may be required to hold the magnet in place while the bonding material cures. Close production control over cure schedule and joint surface preparation is necessary in order to achieve an adhesive bond of optimum properties.